(RFE/RL) -- The leaders of the world's biggest economies ended their first day at the Group of Eight (G8) summit with an agreement to support major emission reduction targets to confront global warming.

The move, which was opposed by the Bush White House, is a significant step in the battle to halt climate change.

Leaders agreed to take steps aimed at limiting the Earth’s average temperature from rising more than 2 degrees Celsius above pre-industrial levels by 2050.

That’s the threshold at which climate-change experts say catastrophic changes stemming from hotter world temperatures might still be avoided. The slightest increase in temperature beyond that could lead to rising sea levels, monster storms, and epic droughts, they warn.

British Prime Minister Gordon Brown said the deal lays the groundwork for much wider agreement among nations at the next UN climate conference in Copenhagen in December.

Satisfaction over the consensus was dimmed by a move earlier in the day when negotiators from 17 of the world's worst polluting countries rejected a draft agreement to slash by half the global output of greenhouse gases by 2050. That plan called for industrialized countries to cut emissions by 80 percent, and developing nations to reduce their output by 50 percent.

Signs Of Economic Stabilization

Over three days the meetings will widen to include rapidly growing countries like India, China, and others such as Egypt, Turkey, and Brazil. Nine African countries will participate on the summit's last day, on July 10, as heads of state take on issues like world hunger and aid to the developing world.

The first day of meetings also reportedly brought agreement that the global economy is still too unstable to begin reversing the many massive stimulus plans the major world governments enacted in the last several months.

The Associated Press reported that a draft of a statement says, "The economic situation remains uncertain and significant risks remain to economic and financial stability." The statement goes on to say that the world’s major economies will continue to take individual and collective action to return the global economy to health.

Germany, which is Europe’s biggest economy, has been pressing for more fiscal restraint, while Britain, Japan, and the United States are considering a second round of stimulus packages.

Statement Expected On Iran

At a working dinner on late on July 8, leaders were expected to turn to pressing international political issues like North Korea’s nuclear ambitions and Iran’s postelection turmoil.

G8 foreign ministers meeting in Trieste last month deplored the violence, but in terms that did not specifically criticize Iranian authorities for the deadly crackdown.

RFE/RL's Radio Farda correspondent Ahmad Rafat is covering the summit in the city of L'Aquila, which was devastated by an earthquake in April.

He says any G8 statement on Iran will depend on what was discussed when U.S. President Barack Obama met Russian President Dmitry Medvedev in Moscow earlier this week.

"Here in L'Aquila everyone is waiting to see what was discussed in Moscow because Russia is the only country in G8 that is opposed any condemnation of Iran and supporting Iran," Rafat says.

"As I understand speaking to Italian officials close to [Italian Prime Minister Silvio] Berlusconi, the problem in Moscow was not resolved and Russia is against any hard condemnation of Iran at the G8 summit in L'Aquila."